According to Dalton’s physical law, the total pressure of a mixture of gases is equal to the sum of the partial pressures of the gases that compose it.
The air we breathe is a mixture of gases where 78% is Nitrogen and 21% is Oxygen (O2). This gas is transported to the blood through the diffusion process. The process depends on the difference in gas pressures between the blood capillary and the pulmonary alveolus.
The greater the difference of partial pressures of oxygen between both compartments, the greater the diffusion of O2 towards the blood, increasing its concentration.
According to Henry’s physical law, the amount of gas dissolved in a liquid is directly proportional to the partial pressure exerted by that gas on the liquid. If the pressure of the environment increases in a certain proportion, the pressure of the O2 increases in equal measure. Thus, Oxygen is transported in the blood together with Hemoglobin (Hgb) inside the red blood cells.
Under normal conditions and breathing air at 1 ATM, the Hemoglobin (Hgb) carries 97% of the O2, that is, the red blood cells have their ability to bind to the almost saturated O2. If we increase the concentration of O2 breathed by a mask and we add a pressurized environment (hyperbaric), we increase the diluted O2 in the blood and in all body fluids (blood, lymphatic, articular and cerebrospinal fluid).